With increase of mobile communication network standards, to save sites and location, reduce difficulty of estate management coordination, and decrease investment cost, multi-frequency shared antenna sharing a common site and location is eventually becoming a first choice for operators in networking business.
Currently in this industry, two constructions are mainly employed to multi-frequency shared antennae array. One solution is coaxial nesting as denoted in FIG. 1. According to this solution, a low frequency radiation unit 1a and a high frequency radiation unit 2a are coaxially arranged on a same axis 4a of a reflection plate 3a. Another solution is side by side adjoining solution as shown in FIG. 2. In this solution, a low frequency radiation unit 1b and a high frequency radiation unit 2a are separately disposed on two adjacent axes 4b and 5b of a reflection plate 3b. Needless to say, the axial nesting scheme significantly has smaller antenna width and windward area than side by side scheme and accordingly, it gets much favor from clients.
It has been found in practice that coaxial nesting technique shown in FIG. 1 suffers from certain limit during use and there are at least two drawbacks.
At first, in case that pitch between low frequency radiation units 1a arranged in line with the high frequency radiation units 2a is not integer times of pitch between high frequency radiation units 2a, in an orthogonal projection area formed by orthogonally projecting onto the reflection plate, radiation arms of the low frequency radiation unit 1a, which is enable to nest with the high frequency radiation unit 2a, will be over the high frequency radiation unit 2a and overlap and cross with the same (as shown in FIG. 3, the low frequency radiation unit 1c crosses and overlaps with the high frequency radiation unit 2c), thus causing severe interference to high frequency radiation array formed by said high frequency radiation unit 2a, and greatly increasing difficulty in design of high frequency radiation array radiation characteristics. For example, when coaxial nesting technique applies to multi-frequency shared electrically adjustable antenna working at frequency of 790˜960 MHz and 1710˜2690 MHz, to make balance between gain and parameters such as electrically down-tilted upper side-lobes, pitch range of low frequency radiation array is normally from 250 mm to 300 mm, while pith range of high frequency radiation array is normally from 105 mm to 115 mm. No matter what sort of array pitch is selected from above ranges for high and low frequency, when all the high frequency radiation units 2b and low frequency radiation units 1b are coaxial, radiation arms of some low frequency radiation units 1b will locate over the high frequency radiation units 2b, thereby causing severe interference to high frequency radiation units 2b, and greatly increasing difficulty in design of high frequency radiation array radiation characteristics. Attempts have been made to overcome this problem by reducing projection area of the low frequency radiation units 1b. However, this will also increase half-power beam width in horizontal plane of the low frequency radiation units 1b and therefore no desired results may be obtained.
Secondly, it may be applied into triple electrically adjustable antenna constructed of a low frequency radiation array and two identical high frequency radiation arrays. Regarding this point, there are two prior art solutions. One is shown in FIG. 4 where a group of high frequency radiation arrays is added to an antenna along a vertical direction. The shortcoming of this solution lies in substantial increase in antenna length. Further, transmission loss as well as antenna gain loss is increased due to lengthening of main feeder line of upper high frequency radiation array. A second solution is illustrated in FIG. 5 where a group of high frequency radiation arrays is added to an antenna at a lateral side thereof. This solution suffers from shortcoming such as substantial increase of antenna width. In addition, all the low frequency radiation arrays are distributed at a side of the high frequency radiation arrays. Due to dramatic asymmetry between left and right radiation boundary of the low and high frequency radiation arrays together with cross-interference between the two arrays, problem such as direction deflection of horizontal plane beam of the two arrays and cross polarization ratio deterioration arises. This results in increased difficulty in design.